The present invention pertains to the art of aligning one or more surfaces with respect to a reference surface and, in particular, to a method and apparatus for aligning the instrument bearing platforms of an aircraft with respect to the axes of the aircraft.
There is a need in the commercial aircraft art to align various instrument bearing platforms, or trays, positioned at various locations within the aircraft with respect to the aircraft's axes. Without such alignment, the indications from these instruments, such as guidance related systems, might prove erroneous.
FIG. 1 is a cutaway view of an aircraft's fuselage 10. Shown is the floor 12 of the aircraft in which are formed seat track pairs 14, 16. In the present example, the aircraft body structure is fabricated to tooling which indexes to the seat tracks 14, 16. Thus, the plane defined by the seat tracks 14, 16 is inherently a plane of zero roll, pitch and azimuth with respect to the axes of the aircraft.
An instrument platform 20 mounts to brackets 22 within an equipment housing 24 accessed through the fuselage 10. In this instance, platform 20 supports, via alignment brackets 26, the inertial reference equipment (not shown) of the aircraft's navigation equipment. It is imperative for proper operation of the inertial reference equipment that the platform 20 be aligned with respect to the three axes of the aircraft. It should be noted that the platform 20 is capable of rotating about a stud 28, the axis of which is perpendicular to the azimuth plane of platform 20.
An equipment tray 30 is supported by a bracket 32 which mounts to the bulkhead 34 of the aircraft. In the present instance, tray 30 supports, via alignment brackets 36, the aircraft's weather radar equipment. As with platform 20, it is imperative that tray 30 be aligned with respect to the pitch, roll and azimuth axis of the aircraft to assure proper output readings from the weather radar equipment. Tray 36 is accessible by raising the radome 40 of the aircraft.
The prior art approach to indexing the target platforms 20, 30 with respect to the three aircraft axes is understood as follows.
An alignment tray tool 50 is affixed to a seat track pair, such as pair 14. Affixed to tool 50 is telescope 52 and alignment tray brackets 54, both of which are seen more clearly with respect to FIG. 3.
A pair of longitudinal sight targets 60, 62 are positioned at spaced intervals towards the forward portion of the aircraft and are affixed to the first seat track pair 14. A cross hair (not shown) is provided within the sight portions 64, 66 of the sights 60, 62.
In addition, a sight target 68, also having a cross hair provided within a sight 70, is mounted opposite tool 50 and affixed to the second seat track pair 16.
An operator, viewing through the telescope 52, aligns cross hairs provided in his telescope with the cross hairs of the sight targets 60, 62 and 68. Suitable adjusting means (more clearly shown with respect to FIG. 3) provided on the alignment tray tool 50 allows the operator to adjust the pitch, roll and azimuth of this tool. In this way, by aligning the telescope with the target sights, the operator establishes that the telescope and, thus, the mounting surface of the alignment tray tool 50 are in a plane parallel with the axes of the aircraft.
At this point, a gyroscopic reference system 70 is mounted to the aligning brackets 54 of the alignment tray tool 50. After a stabilization period, null sensing galvanometers are set to "zero" reference for the gyroscopic reference system of pitch, roll and azimuth. The gyroscopic reference system 70 is then physically removed from the alignment tray tool 50 and carted to the location of the inertial reference platform 20. It is then mounted to the aligning brackets 26 of platform 20 and given time to stabilize. After the stabilization period, the pitch and roll of platform 20 are adjusted by peelable shins, such as shims 72, provided under each corner of the platform until the indicated pitch and roll readings from the gyroscopic reference unit 70 agree with the null readings taken on the alignment tray tool 50. After pitch and roll are adjusted, the platform 20 is rotated about the stud 28 until the azimuth reading of the gyroscopic reference unit 70 agrees with the null reading taken on the alignment tray tool 50. In this manner, platform 20 is aligned with respect to the axes of the aircraft.
Finally, the gyroscopic reference unit 70 is removed from platform 20 and carted to the vicinity of tray 30. There it is mounted to tray 30 via the alignment brackets 36, and the pitch, roll and azimuth of tray 30 are adjusted in the same manner as was used to adjust platform 20.
The aforedescribed technique for aligning the aircraft instrument bearing platforms suffers from numerous problems, most of which relate to the gyroscopic reference unit. This unit is extremely expensive and very fragile. It is not uncommon for the unit to suffer impact while it is being moved between mounting positions. This impact may cause errors in the equipment, whereby the procedure must be reinstituted or may result in possible damage to the unit itself.
In addition, the gyroscopic units require a lengthy time to stabilize, both during "spin up" and "spin down" whereby the aforedescribed platform aligning technique is extremely time consuming.